A light-emitting element included in an image forming device degrades as it emits light. Thus, the amount of emitted light is reduced with use. If the amount of emitted light is reduced, the amount of emitted light from each light-emitting element of a light-emitting unit becomes non-uniform and print quality decreases. Accordingly, it is preferable that the amount of emitted light from each light-emitting element is uniformly maintained.
A method of uniformly adjusting the amount of emitted light of the entire light-emitting elements may be utilized. For example, drive currents of each light-emitting element may be controlled based on the amount of emitted light when each light-emitting element that is measured emits light. As another example, drive currents of each light-emitting element may be controlled based on characteristic data of a cumulative drive time and the amount of emitted light of each light-emitting element. As another example, data opposite to data which forms an electrostatic latent image may be generated, thus making each light-emitting element emit light, and thereby aligning a light emission time of each light-emitting element.
However, increasing the amount of emitted light from a light-emitting element via the drive current further accelerates degradation of the light-emitting element. In addition, using light emission from the light-emitting element for aligning a light emission time of the light-emitting element can also advance degradation of the light-emitting element.